The bigger part of Ripple validator Docker code was kept from Wietse Wind's code from GitHub (https://github.com/WietseWind/docker-rippled-validator).
- Add WORKDIR directive (WORKDIR /keystore) to take away creation of two directories in entrypoint script.
- Order packages needed in alphabetic order for better visibility.
- Suggest removing SSH package from first RUN directive.
- Maybe move mkdir command (for .ripple directory) from entrypoint script to the first RUN directive.
- Use LABEL directive instead of MAINTAINER (deprecated).
- Update syntax to comply to new Docker engine (docker run vs docker container run etc.) and update "How to use this?".
- Maybe map db files to a local filesystem (NuDB files).